Method and system for aligning printheads that eject clear ink in an inkjet printer

Abstract

A method enables an operator to detect misalignment of printheads that eject clear ink in an inkjet printer. The method prints a first test pattern with a first color of ink and then prints a second test pattern of clear ink on top of the first test pattern. The ink of the first and the second test patterns is then spread to enable the clear ink to be dispersed in interstitial spaces in the ink of the first color. An operator is then able to detect the spatial relationship of predetermined marks in the second test pattern to predetermined marks in the first test pattern. The predetermined marks of the first and the second test patterns are arranged to enable an operator to detect a misalignment distance and the inkjet printer uses the misalignment distance entered by the operator to adjust the alignment of the printheads that eject clear ink.

What is claimed: 
     
       1. A method of aligning printheads that eject clear ink in an inkjet printer comprising:
 printing a first test pattern with ink having a first color on recording media as the recording media moves in a process direction past at least one printhead that ejects the ink having the first color, the printing of the first test pattern including printing a plurality of rows of a first predetermined mark on the recording media with ink drops of the first color separated from one another by at least one pixel position in a cross-process direction; 
 printing a second test pattern with clear ink on the recording media as the recording media moves in the process direction past at least one printhead that ejects the clear ink, the second test pattern being printed over the first test pattern and the printing of the second test pattern including printing a plurality of rows of a second predetermined mark on the recording media with clear ink drops positioned between the ink drops of the first color, the second predetermined mark being different than the first predetermined mark; 
 receiving data identifying a distance indicative of a misalignment of the at least one printhead that ejects the clear ink, the distance corresponding to a position of a portion of the second test pattern on the recording media; and 
 operating with a controller at least one actuator operatively connected to the at least one printhead that ejects clear ink, the controller operating the at least one actuator with reference to the misalignment identifying data to adjust alignment of the at least one printhead that ejects clear ink with reference to the at least one printhead that eject the ink having the first color. 
 
     
     
       2. The method of printhead alignment in  claim 1  further comprising:
 printing the plurality of rows of the first predetermined mark with a center of the first predetermined marks being separated by a first distance; and 
 printing the plurality of rows of the second predetermined mark with a center of the second predetermined marks being separated by a second distance, the first distance being different than the second distance. 
 
     
     
       3. The method of printhead alignment in  claim 1  wherein the first predetermined mark is substantially rectangular and the second predetermined mark is a cruciform. 
     
     
       4. The method of printhead alignment in  claim 1  wherein the first predetermined marks in the plurality of rows also being arranged in a plurality of columns in the process direction; and
 the second predetermined marks in the plurality of rows also being arranged in a plurality of columns in the process direction. 
 
     
     
       5. The method of printhead alignment in  claim 1  wherein the data identifies a distance indicative of at least one of a cross-process misalignment and a process direction misalignment. 
     
     
       6. The method of printhead alignment in  claim 1 , wherein the data identifies a distance indicative of a roll misalignment. 
     
     
       7. The method of printhead alignment in  claim 1  further comprising:
 spreading the first test pattern and the second test pattern on the recording media before the identifying data is received. 
 
     
     
       8. The method of printhead alignment in  claim 1  further comprising:
 printing with the ink having the first color a plurality of objects having a predetermined length in a cross-process direction, the objects printed in the ink having the first color being separated from each other by a predetermined distance in the process direction; and 
 printing with the clear ink a plurality of objects having the predetermined length in the cross-process direction, the objects printed in the clear ink being separated from each other by a predetermined distance in the process direction that is different than the predetermined distance separating the objects printed in the ink having the first color. 
 
     
     
       9. The method of printhead alignment in  claim 8  wherein the objects printed in the ink having the first color and the objects printed in the clear ink being rectangles and the rectangles printed in the clear ink are printed over the rectangles printed in the ink having the first color. 
     
     
       10. The method of printhead alignment in  claim 1  wherein the clear ink of the second test pattern is printed within interstitial spaces in the first test pattern to enable specular reflection of light from the recording media. 
     
     
       11. An inkjet printer comprising:
 at least one printhead having an array of inkjets from which ink having a first color is ejected; 
 at least one printhead having an array of inkjets from which clear ink is ejected; 
 a user interface through which data is entered for processing within the inkjet printer; 
 at least one actuator operatively connected to the at least one printhead that ejects clear ink; and 
 a controller operatively connect to the at least one printhead that ejects ink having the first color, the at least one printhead that ejects clear ink, the at least one actuator, and the user interface, the controller being configured: 
 to operate the at least one printhead that ejects ink having the first color to print a first test pattern with ink having the first color on recording media moving in a process direction past the at least one printhead that ejects the ink having the first color, the first test pattern having a plurality of rows of a first predetermined mark on the recording media with ink drops of the first color separated from one another by at least one pixel position in a cross-process direction; 
 to operate the at least one printhead that ejects clear ink to print a second test pattern with clear ink on the recording media as the recording media moves in the process direction past at least one printhead that ejects the clear ink, the controller operating the at least one printhead that ejects clear ink to print the second test pattern over the first test pattern, the second test pattern having a plurality of rows of a second predetermined mark on the recording media with clear ink drops positioned between the ink drops of the first color, the second predetermined mark being different than the first predetermined mark; and 
 to receive from the user interface data identifying a distance indicative of a misalignment of the at least one printhead that ejects the clear ink, the distance corresponding to a position of a portion of the second test pattern on the recording media, and to operate the at least one actuator operatively connected to the at least one printhead that ejects clear ink, the controller operating the at least one actuator with reference to the misalignment identifying data to adjust alignment of the at least one printhead that ejects clear ink with reference to the at least one printhead that ejects the ink having the first color. 
 
     
     
       12. The inkjet printer of  claim 11 , the controller being further configured to print the plurality of rows of the first predetermined mark with a center of the first predetermined marks being separated by a first distance and to print the plurality of rows of the second predetermined mark with a center of the second predetermined marks being separated by a second distance, the first distance being different than the second distance. 
     
     
       13. The inkjet printer of  claim 11 , the controller being further configured to print the first predetermined mark as substantially rectangular and the second predetermined mark as a cruciform. 
     
     
       14. The inkjet printer of  claim 11 , the controller being further configured to operate the at least one printhead that ejects ink having the first color to print the first predetermined marks in the plurality of rows in a plurality of columns in the process direction and to operate the at least one printhead that ejects clear ink to print the second predetermined marks in the plurality of rows in a plurality of columns in the process direction. 
     
     
       15. The inkjet printer of  claim 11 , the controller being further configured to print the first predetermined marks in the plurality of rows in a plurality of columns in the process direction and to print the second predetermined marks in the plurality of rows in a plurality of columns in the process direction. 
     
     
       16. The inkjet jet printer of  claim 15 , the controller being further configured to print the objects with the ink having the first color a plurality of objects with a predetermined length in a cross-process direction, the objects printed in the ink having the first color being separated from each other by a predetermined distance in the process direction and to print the objects with the clear ink a plurality of objects with the predetermined length in the cross-process direction, the objects printed in the clear ink being separated from each other by a predetermined distance in the process direction that is different than the predetermined distance separating the objects printed in the ink having the first color. 
     
     
       17. The inkjet printer of  claim 16 , the controller being further configured to print the objects in the ink having the first color and the objects in the clear ink as rectangles and to print the rectangles printed in the clear ink over the rectangles printed in the ink having the first color. 
     
     
       18. The inkjet printer of  claim 11  wherein the controller is further configured to operate the at least one actuator with reference to the data that identifies the distance indicative of misalignment to move the at least one printhead that ejects clear ink in at least one of a cross-process direction and a process direction. 
     
     
       19. The inkjet printer of  claim 11 , wherein the controller is further configured to operate the at least one actuator with reference to the data that identifies the distance indicative of misalignment to move the at least one printhead that ejects clear ink in one of a clockwise rotational direction and a counterclockwise rotational direction. 
     
     
       20. The inkjet printer of  claim 11  further comprising:
 a spreader positioned from the at least one printhead that ejects the ink having the first ink color and the at least one printhead that ejects the clear ink in the process direction, the spreader being configured to spread the ink having the first color and the clear ink on the recording media before the identifying data is received. 
 
     
     
       21. The inkjet printer of  claim 11 , the controller being further configured to eject the clear ink of the second test pattern within interstitial spaces in the first test pattern to enable specular reflection of light from the recording media.